His name is already found in Homer (Il., XV, 36; Od., V, 184), but he appears as a protagonist in Hesiod’s Theogony, where he is the spouse of Gaia (the Earth) and father, among other deities, of the Titans (v.) and the Cyclopes (Th., 126 ff.). However, jealous of his children, U. hid them within the earth until they, incited by Earth, rebelled; then Saturn, treacherously, castrated U., and the severed parts falling into the sea gave birth to Aphrodite. Some texts differing from the Theogony call him: "Akhmon" as sky, and this allusion is taken up poetically by Antimachus (Ἀχμονίδης, fr. 35 Kinkel) and by Alcman (Ἀχμονίων, fr. 111 Bergk). Other sources, instead, interpret this epithet as ἀχμάτος, indefatigable (v. L. Preller-C. Robert, Griechische Mythologie, I, 4th ed., Berlin 1894, p. 39, note 3). The cult of U., neglected in Olympian religion, came back into honor in the Hellenistic period, perhaps under earlier Orphic influence. The frieze in bas-relief of the Pergamon Altar also includes U. fighting against a giant.
In Roman religion U. is venerated under the name Caelus (ὁ Qui si est deus [Saturnus], patrem quoque eius Caelum esse deum confitendum est *: Cicero, Nat. deor., III, 17, 44). Art depicts him in a chariot, holding a cloak arched above his head (ἀλθόρος χύλλος). In this manner he is portrayed on the cuirass of the statue of Augustus found at Prima Porta, and this representation continues in the iconography of the early Church (v. Jahn, Arch. Beitr., 85, p. 28; id., in Ber. d. Sächs. Gesellschaft, d. Wissenschaft, 1849, p. 63).